Ultrasonication as pretreatment for drying of tomato slices in a hot air–microwave hybrid oven

This study aims to investigate the effect of ultrasonic pretreatment on drying time and quality properties of tomato slices dried by microwave combined with hot air at 60°C. The influence of ultrasound pretreatment (0, 20, and 40?min) and microwave power (120, 150, and 180?W) on drying time, color, total phenolic content, lycopene, vitamin C, and rehydration capacity of dried slices of tomato was studied. Results showed that as the microwave power level increased, drying time decreased significantly (about 46.4%). Ultrasound pretreatment decreased the drying time by 7.38% only at 120?W microwave power and 40?min of pretreatment compared to those without ultrasound pretreatment at the same microwave power. Depending on drying conditions, vitamin C and lycopene contents reduced from 433.94 to 81.89?mg AA/100?g dry solids and 3920.57 to 415.40?mg/100?g dry solids, respectively. The change in total phenolic content was not severe as much as vitamin C contents. Rehydration capacity of pretreated samples was larger than nontreated samples. The color values of dried tomato slices were in the acceptable range. Both microwave power and ultrasound pretreatment affected the quality of the final product significantly.     

Synthesis of SiC–TiO2 hybrid aerogel via supercritical drying combined PDCs route

The SiC-TiO₂ hybrid aerogels were obtained from polycarbosilane (PCS) and tetrabutyltitanate (TBT) as precursors using supercritical drying and polymer derived ceramics route. The polymer to ceramic conversion and the crystallization behavior were studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM), suggesting the preceramic aerogels converted to the SiC-TiO₂ ceramic aerogels through pyrolysis process at different temperatures. At 1200 °C, the ceramic aerogels were homogeneous with well-distributed element components, composed of rutile TiO₂ and the β-SiC crystalline phases. The results show that the SiC-TiO₂ ceramic aerogels with netwoks structure have 23.36 nm average pore size, high surface area (58 m²/g) and pore volume (0.22 cm³/g).     

Through air drying of paper—the effect of dryer fabric

A custom experimental apparatus is designed to perform through air drying under well-controlled drying conditions such as air temperature and mass-flowrate. Using a novel optical measurement technique, the spatial distribution of moisture content in paper during through air drying is quantified as a function of time. The technique is capable of measuring the moisture content distribution with high spatiotemporal resolution while air flows through a paper mat sitting on a permeable dryer fabric. Four commercially available fabrics with different structural design and properties are used in the investigations. The effect of the fabrics’ structural properties, which are characterized using optical coherence tomography (OCT), is studied under various drying conditions. It is shown that the geometry of the contact spots of the fabrics has a significant impact on the drying time at high drying intensities. However, at low rates of drying (i.e., low air temperature and flowrate), no correlation between drying time and fabric properties is observed. After a cycle of through air drying, the permeability of paper increases irreversibly. This increased permeability is observed to be a function of the fabric structure. It is shown that the increase in permeability is larger for coarse fabric structures although no monotonic correlation with the fabric permeability can be observed. Comparing the spatial maps of moisture content with the paper grammage distribution reveals that there is a correlation between the local grammage and the spatial pattern of drying in a paper sheet.     

Explosion of gas–air mixtures in coke production

The combustion temperatures of mixtures of 43 highly inflammable and combustible liquids with air are determined at constant volume, at concentrations corresponding to the upper and lower limits on flame propagation in conditions of constant pressure. The results show that these temperatures are approximately the same for different materials. The combustion temperatures of air–vapor mixtures containing a safe (according to handbook data) concentration of retardant may exceed that of the limiting compositions. This raises doubts regarding the validity of handbook data obtained in tests in small chambers. The limiting combustion temperatures of mixtures containing air and the gases and vapor formed in coke production are calculated; these results are required for reliable determination of the retardant concentrations of inert gases.     

Modeling heat and mass transfer–induced stresses in germinated brown rice kernels during fluidized bed drying

A study of stress distribution inside a germinated brown rice (GBR) kernel during drying is important to understand the fissure formation of GBR and hence control the drying process in order to improve the quality of GBR. In this study, a finite element method performed in three dimensions in conjunction with the heat and mass balance of the drying system was developed to describe moisture, temperature, and stress distributions inside GBR kernels during fluidized bed drying. The modeling was carried out using the coupling of heat and mass transfer and validated with experimental data at 90–150°C. The results of moisture and temperature predictions agreed well with the experiments. During drying, tensile stress occurred at the layers close to surface and compressive stress occurred at the inner portion of a kernel. The tensile and compressive stresses increased to the highest value at about 30 s of drying, corresponding to the highest moisture gradient, and then decreased afterwards. The tensile and compressive stresses were higher at a higher drying temperature. These stress prediction results corresponded to the experiments, which show more severe GBR fissuring at higher drying temperatures.     

Adsorption-mediated nonlinearity of critical cracking thickness in drying nanoparticle–polymer suspensions

We examine the critical cracking thicknesses of as-dried colloidal TiO₂ suspensions containing water-soluble polymeric additives, above which cracks spontaneously propagate. In contrast to common observations, the critical cracking thickness increases in a nonlinear, stepwise manner as increasing the concentration of the polymeric additive in the suspension. The critical thickness diverges when the polymer content increases above a certain threshold. We demonstrate that the first and second critical cracking thickness increments are attributable to the onset of polymer adsorption and a subsequent transition in the conformations of the adsorbing polymer chains, respectively. The critical thickness profiles with respect to normalized polymer adsorption amounts at different particle diameters converged into a single master curve. These results illustrate nontrivial evaporation processes in which the various roles of polymeric additives delay cracking into thicker films.     

Flow patterns and gas fractions of air–oil and air–water flow in pipe bends

An experimental study of two-phase flow in a 180° pipe bends with 0.016, 0.022 and 0.03 m and the curvature radii of 0.11, 0.154, 0.21 m, respectively have been carried out. The experiments were conducted under the input superficial phase velocity: air from 0.038 to 5.4 m s⁻¹, water from 0.018 to 0.92 m s⁻¹ and oil from 0.014 to 0.92 m s⁻¹. The conducted research involved the observation of the forming flow patterns and determination of average volumetric in situ gas fraction. On the basis of the results of experimental flow map was created for gas–liquid flow and a method of calculating gas fractions was established.     

Ignition of a two-fuel hydrogen–silane mixture in air

Based on the previously developed model of detailed kinetics, the ignition delay time of two-fuel hydrogen–silane–air mixtures is calculated. The effect of the silane concentration and the temperature of the mixture on the ignition delay time is determined. It is shown that addition of a small (within 20%) amount of silane to the hydrogen–air mixture in the temperature range from 1200 to 2500 K leads to significant reduction of the ignition delay time of the mixture, whereas there is only a minor decrease in mixtures with silane concentrations higher than 20%.     

Combustion and detonation of propane–air compositions in large-scale experiments

This paper presents the results of two large-scale tests performed to clarify the conditions for the detonation of propane–air compositions in model surface clouds in the absence and in the presence of confining rigid walls. Model clouds with dimensions of 15 × 6 × 4.2 and 15 × 6 × 2 m were confined by plastic tents. A mixture of the starting reagents in the cloud was ignited by hot detonation products propagating along a perforated ø0.82 × 23 m tube passing through the space of the tent. Hot detonation products were injected from the tube through holes of 20 and 40 mm diameters. Detonation of the propane-air mixture in the tube was initiated by explosion of an explosive charge placed at the tube end. Detonation occurred in the propane–air cloud bounded on one side by a rigid vertical wall, and no detonation was observed in the cloud with similar injection of hot products without a rigid wall. It is concluded that the divergence or convergence of the flows of hot detonation products plays a key role in the process, being responsible for the presence or absence of detonation, respectively, in the mixing region.     

Ignition of the drops of coal–water fuel in a flow of air

The ignition of the drops of coal–water fuel (CWF) in a high-temperature gas (air) flow was experimentally studied. The conditions and fundamental characteristics of the ignition (ignition delay times) were found. The effects of a number of factors (drop sizes and ambient temperatures) on the conditions of ignition were examined. Based on the results of experiments, a physical model was formulated for the processes of thermal preparation and ignition of CWF drops. The experimental delay times of the ignition of CWFs were compared with the theoretical values (obtained with the use of a previously developed mathematical model).     

Modeling ultraviolet dose–response of Bacillus spore clusters in air

This article presents a new way to model the narrow band ultraviolet (UV-C, 254.7 nm) radiation dose–response behavior of Bacillus spores in clusters based on knowledge of the UV-C dose–response behavior of the single spores. The approach is demonstrated using experimentally obtained survival rates for Bacillus atrophaeus var. globigii (BG) spores and BG spore clusters of several sizes exposed to UV-C fluence when aerosolized and when deposited on dry surfaces. These results are modeled to derive predicted survival rates for spores in clusters of arbitrary cluster diameter under similar conditions. The essential feature of the approach is accurate accounting for attenuation of incident UV fluence within the spore cluster to derive the fluence incident on individual spores within the cluster. The results suggest that UV fluence attenuation by bacterial spores may increase with increasing fluence, a phenomenon that has not been previously reported for bacterial spores. The results are of utility in estimating dispersed biological hazards and evaluating the effectiveness of ultraviolet germicidal irradiation (UVGI) systems.

Copyright © 2016 American Association for Aerosol Research     

Scaling factor in continuous spin detonation of syngas–air mixtures

Multiwave regimes of continuous spin detonation in syngas–air mixtures in a flow-type annular cylindrical combustor 503 mm in diameter are obtained. Experiments are performed for mixtures of carbon oxide and hydrogen with the ratio of the components equal to 1/3, 1/2, or 1/1. The varied parameters are the flow rates of air and syngas, the ratio of these flow rates, and the combustor length. Scalability of the continuous spin detonation process is demonstrated: at identical values of the specific flow rate of air and the combustor expansion ratio, the number of transverse detonation waves increases with increasing combustor diameter. In the examined ranges of combustor lengths and specific flow rates of air, the frequency of these waves is independent of the combustor length, except for narrow regions where the number of waves (and, correspondingly, the flow regime) changes. The structures of transverse detonation waves in regular regimes are almost identical for all examined syngas compositions. It is shown that detonation can be initiated by a jet of combustion products. The minimum diameters of the detonation chamber for different flow rates of the mixture are estimated.     

Oxidation mechanism of MgO–C in air at various temperatures

Abstract

Oxidation of MgO–C refractories containing 20 wt-%graphite was conducted by measuring the weight loss at regular intervals at various temperatures from 800 to 1600°C in air. The rate of decarburisation increased with rise in temperature from 800 to 1400°C and then remained more or less constant from 1400 to 1600°C. The oxidation kinetics were analysed in detail and reaction rate models derived for the temperature range 800–1400°C. The reaction rate was found to be controlled by diffusion of oxygen through the decarburised layer. At higher temperatures (>1400°C), oxidation of graphite also takes place indirectly by the reaction MgO(s) + C(s) → Mg(g) + CO(g). The magnesium vapour thus produced is reoxidised at the outer surface and redeposited as MgO. This leads to a reduction in porosity in the decarburised outer shell and, consequently, a reduction in the rate of oxidation.     

Change in reactivity of kerogen-containing rock samples in air at temperatures of 450–650 K

Experiments on studying chemical interaction of kerogen-containing rock samples with an atmospheric air flow are described. The crushed rock was placed into a flow reactor with a controlled heating temperature. The fact of rock interaction with oxygen contained in air was detected by a gas analyzer, based on changes in the relative concentrations of O₂ and CO₂ molecules in the gas flow at the reactor exit. The measurements are performed in the temperature range from 450 to 650 K. The lower limit of temperatures is found (480 K), at which the change in the gas composition is still observed. The change in the chemical activity of the rock bed is estimated under the assumption of a first-order reaction in terms of the oxidizer concentration; the activation energy of the process is found to be 12 kcal/mole.     

Factors controlling the mechanical behavior of alumina–magnesia–carbon refractories in air

This work analyzes the mechanical behavior of alumina-magnesia-carbon (AMC) refractories in air up to 1260 °C. AMC refractory bricks are used on sidewalls and bottoms working linings of steel-making ladles. In plant, AMC bricks are exposed to air atmosphere during the periods of time when the ladle is empty, such as preheating. Stress–strain relationships were determined in compression, and the following parameters were calculated from these curves: strength, apparent Young's modulus, fracture strain and yield strength. Young's modulus at room temperature was also determined by the impulse excitation technique. To identify the main determining factors, the tested specimens were analyzed by apparent porosity measurements, X-ray diffraction and scanning electron microscopy coupled with X-ray dispersive energy. Thermodynamic simulations of the AMC refractories were also performed using FactSage software, so as to understand the mineralogical changes that occur in the refractories as temperature increases.     

Phase equilibria study of K–O–Si system in equilibrium with air

The binary phase diagram in the silica rich corner of K–O–Si system in equilibrium with air has been studied at temperatures between 770 °C and 1500 °C. Equilibration at high temperature in an appropriate containment material of pure silica, followed by rapid quenching and measurement of phase structures and assemblages using SEM-EDS confirmed by an electron probe X-ray microanalysis technique, was carried out to obtain the phase composition data at equilibrium. The results are in good agreement with previous experimental data and close to the earlier assessed phase equilibria at silica saturation.     

Unsteady aspects of sodium–water–air reaction

One important issue for the Sodium Fast Reactor (SFR) concept is the reactivity of metallic sodium and its exothermal reaction with water. In particular during equipments washing operations, sodium needs to be firstly converted (‘destroyed’) into non reactive species via a chemical reaction with water. Today, such operations are performed in tanks that confine the system and mitigate the consequences of any possible abnormal condition.     

New structures of thin air cathodes for zinc–air batteries

Thin composite cathodes for air reduction were manufactured using microfibre-based papermaking technology. The electrodes have a thin structural design, less than 0.15 mm in thickness. Composite cathode materials for oxygen reduction applications were fabricated by entrapping carbon particles in a sinter-locked network of 2–8 m diameter metal fibres. The thin structure not only results in electrodes that are 30–75% thinner than those commercially available, but also offers an opportunity for custom-built air cathodes optimized for high-rate pulse applications. Using a thin composite structure for the air cathode in a zinc–air battery that is part of a zinc–air/capacitor hybrid is likely to increase the pulse capability of the hybrid power system. The thin cathode structure provides a better, more efficient three-phase reaction zone. In a half-cell test, the ultrathin air cathode generated more than 1.0 V vs Zn/ZnO for a current of 200 mA cm^–2. Half-cell, full-cell and pulse-power tests revealed that thin composite cathodes have a better rate and pulse performance than the air cathodes commonly used.     

Influence of convective intermittent drying schemes on drying induced stress–strain of a 3D clay object

Drying process of industrial green in-process products especially those susceptible to cracking, need great care, and optimally arrangement of parameters of convective drying. Intermittent drying is a new technique in drying area and is a promising solution for product quality enhancement. The intermittent drying with variable air temperature and the intermittent drying with variable air humidity are the most used techniques. The current study is devoted to 3D modeling and simulation of intermittent drying with variations of both air humidity and temperature and it is then compared with each of the cases of the intermittent drying with variable air temperature and the intermittent drying with variable air humidity. It was observed that the best dried product quality was obtained in intermittent drying with periodic changes of air temperature. Vapor condensation in the intermittent drying with variable air humidity is an undesirable phenomenon that significantly reduces the effectiveness of this process.     

Thermal hydraulic characteristics of air–water two-phase flows in helical pipes

Helically coiled heat exchangers, where one of the working fluids is flowing through helical coil, are used in various process industries due to better heat transfer characteristics and the resulting compact layout. Out of these, process requirements make some of the heat exchangers to operate in air–water two-phase region. Even though the characteristics of their operation with single-phase working fluids are well documented, it is not so for the case of two-phase flows. There do exist few experimental results on hydrodynamics of air–water flow through helical pipes. However numerical investigation, which can give much insight into the physics of the problem, is lacking and this is the subject matter of this paper.